Ultrasonic instruments, including both hollow core and solid core instruments, are used for the safe and effective treatment of many medical conditions. Ultrasonic instruments are advantageous because they may be used to cut and/or coagulate organic tissue using energy in the form of mechanical vibrations transmitted to a surgical end effector at ultrasonic frequencies. Ultrasonic vibrations, when transmitted to organic tissue at suitable energy levels and using a suitable end effector, may be used to cut, dissect, elevate or cauterize tissue or to separate muscle tissue off bone. Such instruments may be used for open procedures or minimally invasive procedures, such as endoscopic or laparoscopic procedures, wherein the end effector is passed through a trocar to reach the surgical site.
Activating or exciting the end effector (e.g., cutting blade) of such instruments at ultrasonic frequencies induces longitudinal vibratory movement that generates localized heat within adjacent tissue, facilitating both cutting and coagulation. Because of the nature of ultrasonic instruments, a particular ultrasonically actuated end effector may be designed to perform numerous functions, including, for example, cutting and coagulation.
Ultrasonic vibration is induced in the surgical end effector by electrically exciting a transducer, for example. The transducer may be constructed of one or more piezoelectric or magnetostrictive elements in the instrument hand piece. Vibrations generated by the transducer section are transmitted to the surgical end effector via an ultrasonic waveguide extending from the transducer section to the surgical end effector. The waveguides and end effectors are designed to resonate at the same frequency as the transducer. Therefore, when an end effector is attached to a transducer the overall system frequency is the same frequency as the transducer itself.
The zero to peak amplitude of the longitudinal ultrasonic vibration at the tip, d, of the end effector behaves as a simple sinusoid at the resonant frequency as given by:d=A sin(ωt)where:    ω=the radian frequency which equals 2πtimes the cyclic frequency, f; and    A=the zero-to-peak amplitude.The longitudinal excursion is defined as the peak-to-peak (p-t-p) amplitude, which is just twice the amplitude of the sine wave or 2 A.
Ultrasonic surgical instruments may be divided into two types, single element end effector devices and multiple-element end effector devices. Single element end effector devices include instruments such as scalpels and ball coagulators. Single-element end effector instruments have limited ability to apply blade-to-tissue pressure when the tissue is soft and loosely supported. Sometimes, substantial pressure may be necessary to effectively couple ultrasonic energy to the tissue. This inability to grasp the tissue results in a further inability to fully coapt tissue surfaces while applying ultrasonic energy, leading to less-than-desired hemostasis and tissue joining. In these cases, multiple-element end effectors may be used. Multiple-element end effector devices, such as clamping coagulators, include a mechanism to press tissue against an ultrasonic blade that can overcome these deficiencies.
Although ultrasonic surgical instruments are widely used in many surgical applications, their utility is limited by their inability to react to tissue and end effector conditions. For example, as the end effector of an ultrasonic instrument is used to coagulate and/or cut tissue, it often heats up. This may cause inconsistencies in the performance of the instrument. Also, there is no way for a clinician using the instrument to know when the instrument has begun to coagulate tissue, when the instrument has begun to cut tissue, or any other information about the tissue.
Another set of drawbacks of ultrasonic instruments stems from existing end effector designs. In the existing designs, only the tip of the end effector (e.g., the blade) is ultrasonically active. Accordingly, tissue contacting the blade more than a fraction of a wavelength from the tip may not be affected at all. Further, because waves must propogate from the transducer to the tip of the end effector, existing end effectors are not very flexible, limiting their ability to articulate and consequently limiting their usefulness in laparoscopic and endoscopic surgical applications.